Beacon height in feet, auto-fill lat/lon from grid

- Rename beacons.height_m to height_ft; migration converts existing
  values (m * 3.28084). Form/list/show labels updated.
- Beacon changeset now fills lat/lon from the grid when they're blank
  (previously only the reverse worked). Lat/lon and grid inputs are no
  longer marked required in the form — enter one side and the other
  populates on blur via phx-change.

lib/microwaveprop/beacons/beacon.ex

@@ -2,7 +2,7 @@ defmodule Microwaveprop.Beacons.Beacon do
   @moduledoc """
   A beacon transmitter. Frequency in MHz, coordinates as lat/lon,
   grid as Maidenhead (auto-computed from lat/lon when not supplied),
-  power in milliwatts, height above ground in meters.
+  power in milliwatts, height above ground in feet.
   """
 
   use Ecto.Schema
@@ -20,26 +20,27 @@ defmodule Microwaveprop.Beacons.Beacon do
     field :lat, :float
     field :lon, :float
     field :power_mw, :float
-    field :height_m, :float
+    field :height_ft, :float
     field :user_id, :binary_id
 
     timestamps(type: :utc_datetime)
   end
 
-  @required_fields [:frequency_mhz, :callsign, :lat, :lon, :power_mw, :height_m]
+  @required_fields [:frequency_mhz, :callsign, :lat, :lon, :power_mw, :height_ft]
 
   def changeset(beacon, attrs) do
     beacon
-    |> cast(attrs, [:frequency_mhz, :callsign, :grid, :lat, :lon, :power_mw, :height_m])
+    |> cast(attrs, [:frequency_mhz, :callsign, :grid, :lat, :lon, :power_mw, :height_ft])
     |> update_change(:callsign, fn cs -> cs && String.upcase(String.trim(cs)) end)
+    |> maybe_fill_latlon()
+    |> maybe_fill_grid()
     |> validate_required(@required_fields)
     |> validate_number(:frequency_mhz, greater_than: 0)
     |> validate_number(:power_mw, greater_than_or_equal_to: 0)
-    |> validate_number(:height_m, greater_than_or_equal_to: 0)
+    |> validate_number(:height_ft, greater_than_or_equal_to: 0)
     |> validate_number(:lat, greater_than_or_equal_to: -90, less_than_or_equal_to: 90)
     |> validate_number(:lon, greater_than_or_equal_to: -180, less_than_or_equal_to: 180)
     |> validate_length(:callsign, min: 3, max: 10)
-    |> maybe_fill_grid()
     |> validate_grid_format()
   end
 
@@ -56,6 +57,27 @@ defmodule Microwaveprop.Beacons.Beacon do
     end
   end
 
+  # If lat/lon are blank but grid is a valid Maidenhead, derive them.
+  defp maybe_fill_latlon(changeset) do
+    grid = get_field(changeset, :grid)
+    lat = get_field(changeset, :lat)
+    lon = get_field(changeset, :lon)
+
+    if is_binary(grid) and grid != "" and (lat in [nil, ""] or lon in [nil, ""]) do
+      case Maidenhead.to_latlon(grid) do
+        {:ok, {new_lat, new_lon}} ->
+          changeset
+          |> put_change(:lat, new_lat)
+          |> put_change(:lon, new_lon)
+
+        :error ->
+          changeset
+      end
+    else
+      changeset
+    end
+  end
+
   defp validate_grid_format(changeset) do
     case get_field(changeset, :grid) do
       nil ->

lib/microwaveprop_web/live/beacon_live/form.ex

@@ -11,7 +11,10 @@ defmodule MicrowavepropWeb.BeaconLive.Form do
     <Layouts.app flash={@flash} current_scope={@current_scope}>
       <.header>
         {@page_title}
-        <:subtitle>Leave the grid blank to auto-fill it from lat/lon.</:subtitle>
+        <:subtitle>
+          Enter either a grid or lat/lon — whichever you leave blank is filled in
+          from the other.
+        </:subtitle>
       </.header>
 
       <.form for={@form} id="beacon-form" phx-change="validate" phx-submit="save">
@@ -23,9 +26,9 @@ defmodule MicrowavepropWeb.BeaconLive.Form do
           required
         />
         <.input field={@form[:callsign]} type="text" label="Call" required />
-        <.input field={@form[:grid]} type="text" label="Grid (auto if blank)" />
-        <.input field={@form[:lat]} type="number" label="Latitude" step="any" required />
-        <.input field={@form[:lon]} type="number" label="Longitude" step="any" required />
+        <.input field={@form[:grid]} type="text" label="Grid" />
+        <.input field={@form[:lat]} type="number" label="Latitude" step="any" />
+        <.input field={@form[:lon]} type="number" label="Longitude" step="any" />
         <.input
           field={@form[:power_mw]}
           type="number"
@@ -34,9 +37,9 @@ defmodule MicrowavepropWeb.BeaconLive.Form do
           required
         />
         <.input
-          field={@form[:height_m]}
+          field={@form[:height_ft]}
           type="number"
-          label="Height above ground (m)"
+          label="Height above ground (ft)"
           step="any"
           required
         />

lib/microwaveprop_web/live/beacon_live/index.ex

@@ -29,7 +29,7 @@ defmodule MicrowavepropWeb.BeaconLive.Index do
         <:col :let={{_id, beacon}} label="Lat">{beacon.lat}</:col>
         <:col :let={{_id, beacon}} label="Lon">{beacon.lon}</:col>
         <:col :let={{_id, beacon}} label="Power (mW)">{beacon.power_mw}</:col>
-        <:col :let={{_id, beacon}} label="Height AGL (m)">{beacon.height_m}</:col>
+        <:col :let={{_id, beacon}} label="Height AGL (ft)">{beacon.height_ft}</:col>
         <:action :let={{_id, beacon}}>
           <div class="sr-only">
             <.link navigate={~p"/beacons/#{beacon}"}>Show</.link>

lib/microwaveprop_web/live/beacon_live/show.ex

@@ -33,7 +33,7 @@ defmodule MicrowavepropWeb.BeaconLive.Show do
         <:item title="Latitude">{@beacon.lat}</:item>
         <:item title="Longitude">{@beacon.lon}</:item>
         <:item title="Power (mW)">{@beacon.power_mw}</:item>
-        <:item title="Height above ground (m)">{@beacon.height_m}</:item>
+        <:item title="Height above ground (ft)">{@beacon.height_ft}</:item>
       </.list>
     </Layouts.app>
     """

priv/repo/migrations/20260408174719_rename_beacon_height_to_ft.exs

@@ -0,0 +1,16 @@
+defmodule Microwaveprop.Repo.Migrations.RenameBeaconHeightToFt do
+  use Ecto.Migration
+
+  # 1 meter = 3.28083989501 feet
+  @m_to_ft 3.28083989501
+
+  def up do
+    rename table(:beacons), :height_m, to: :height_ft
+    execute "UPDATE beacons SET height_ft = height_ft * #{@m_to_ft}"
+  end
+
+  def down do
+    execute "UPDATE beacons SET height_ft = height_ft / #{@m_to_ft}"
+    rename table(:beacons), :height_ft, to: :height_m
+  end
+end

test/microwaveprop/beacons_test.exs

@@ -14,7 +14,7 @@ defmodule Microwaveprop.BeaconsTest do
     lat: nil,
     lon: nil,
     power_mw: nil,
-    height_m: nil
+    height_ft: nil
   }
 
   describe "list_beacons/0" do
@@ -46,7 +46,7 @@ defmodule Microwaveprop.BeaconsTest do
       assert beacon.lat == attrs.lat
       assert beacon.lon == attrs.lon
       assert beacon.power_mw == attrs.power_mw
-      assert beacon.height_m == attrs.height_m
+      assert beacon.height_ft == attrs.height_ft
       assert beacon.user_id == user.id
     end
 
@@ -57,6 +57,19 @@ defmodule Microwaveprop.BeaconsTest do
       assert String.starts_with?(beacon.grid, "EM12")
     end
 
+    test "derives lat/lon from grid when lat/lon are omitted" do
+      user = user_fixture()
+
+      attrs =
+        valid_beacon_attrs(grid: "EM12kp")
+        |> Map.drop([:lat, :lon])
+
+      assert {:ok, beacon} = Beacons.create_beacon(user, attrs)
+      assert beacon.grid == "EM12kp"
+      assert_in_delta beacon.lat, 32.6458, 0.01
+      assert_in_delta beacon.lon, -97.125, 0.01
+    end
+
     test "keeps an explicitly provided valid grid" do
       user = user_fixture()
       {:ok, beacon} = Beacons.create_beacon(user, valid_beacon_attrs(grid: "EM13"))

test/support/fixtures/beacons_fixtures.ex

@@ -12,7 +12,7 @@ defmodule Microwaveprop.BeaconsFixtures do
       lat: 32.897,
       lon: -97.038,
       power_mw: 10_000.0,
-      height_m: 30.0
+      height_ft: 100.0
     })
   end